The present invention relates generally to lead-acid rechargeable batteries and, in particular, to batteries in which bipolar positive and negative plates (biplates) share the same grid or substrate. According to the present invention, such biplates and interleaved, highly porous, glass mat separators are stacked upon each other in such a manner that the substrate positioned between the positive and negative plate areas of the biplates act as electrical connections between adjacent stacks.
Conventional lead-acid batteries are constructed from two volt cells which are usually connected in series. This allows these known batteries (whose nominal voltage is a multiple of two, or "in parallel") to give increased ampere-hour capacity for a combination of series and parallel cells. Each cell contains positive and negative plates separated by, in the case of "flooded" cells, sheets of porous, low resistance, and oxidation resistant materials such as glass, paper, rubber, or polyolefin. In the "flooded" cell, the separator exists merely to insulate adjacent positive and negative plates from each other while providing a low resistance path through which electrons may easily flow. Again, in the flooded cell, free electrolyte exists around the plates contained by the walls of the (plastic or hard rubber cell) container.
In cells known as "starved electrolyte" or "sealed recombinant" cells, the electrolyte is contained in highly porous, relatively thick glass mats interleaved between adjacent positive and negative plates. No "free" electrolyte exists in such cells. The electrolyte required to give the rated electrical energy output is stored within the pores of the separators and the pores of the negative and positive active materials.
The separate positive and negative plates in conventional lead-acid batteries comprise a lead or lead alloy grid, or substrate, into which is impressed a paste. Such substrates are manufactured by one of two methods. In one such method molten lead or an alloy thereof is poured into a mold and frozen. The mold is then opened and the resultant casting is stored for between 24 and 48 hours to allow orientation of metallic grain structure. In another known method, lead, or lead alloy, sheet is slit and expanded to the desired width or length on a continuous basis, and is then cut to the desired size.